API 653 Inspection of On-Stream LPG Storage Tanks

Project Challenge 

Inspecting large double-wall LPG storage tanks under on-stream operating conditions presents significant challenges related to safety, operational continuity, and regulatory compliance. The project required a comprehensive evaluation of structural integrity, corrosion conditions, and safety system functionality while maintaining uninterrupted operation of the LPG terminal.

Project Details 

• Location: LPG Terminal, Chonburi Province, Thailand 
• Asset Type: Double-Wall LPG Storage Tanks 
• Inspection Standards: API 653, API 620 Appendix R, ASME Section V, & ASME Section VIII Division 2 
• Project Duration: 20 days 
• Tank Dimensions: 44.8 m diameter × 35.9 m height 
• Inspection Methods: 
• External Visual Inspection (VT) 
• Ultrasonic Thickness Measurement (UT) 
• Eddy Current Surface Testing 
• Thermography Testing 
• Tank Settlement Survey 
• Plumbness and Roundness Measurements 
• Peaking and Banding Assessment 
• Grounding System Measurement 
• Breather Valve Testing 
• Water Spray Nozzle Testing and Cleaning 
• Monitoring Basis: 5 years 

Engineering Inspection Approach 

Dexon applied an integrated tank integrity assessment methodology, combining non-destructive examination (NDE) data with physical condition surveys and geometric measurements to provide a comprehensive evaluation of tank integrity in accordance with API 653 requirements. 

Engineers assessed wall thickness integrity, structural geometry, and functional safety systems. The inspection included wall thickness measurements, settlement surveys, plumbness and roundness evaluations, structural deformation assessments, coating condition reviews, corrosion inspections, and verification of critical safety systems such as breather valves and firewater spray systems. 

A key advantage of this project was the use of on-stream inspection techniques, allowing the LPG terminal to remain operational throughout the assessment. This eliminated the need for shutdown while still generating sufficient integrity data to support safety evaluations, maintenance planning, and regulatory compliance. 

Dexon also developed damage mapping documentation and a regulatory-ready reporting package to support maintenance prioritization and future regulatory reviews. 

Project Conclusion 

Inspection results confirmed that both LPG storage tanks remain suitable for continued operation.  

Several areas were identified for preventive maintenance planning, including localized coating degradation, isolated corrosion, vegetation growth around drainage systems, and aging sealing materials around tank anchor points. These were classified as maintenance focus areas for future action.